Some cephalosporin compounds which bearing an .alpha.-(substituted imino)-.alpha.-(2-aminothiazolyl)-acetyl group as a side chain at the 7-position and a .beta.-substituted vinyl group as a side chain at the 3-position of the cephem nucleus are known, as disclosed in Japanese Patent Application first publication "Kokai" Nos. 124790/80, 122383/81 and 76088/84, U.K. patent application first publication No. 2128990A and U.S. Pat. No. 4,307,116.
Cephalosporin-type antibiotics are known to be highly and broadly active against a variety of gram-positive and gram-negative bacteria. Various kinds of semi-synthesized cephalosporin compounds have already been available commercially and applied clinically for the therapeutic treatment of various infections diseases. But, only a very few ones amongst these semi-synthesized cepahlosporin compounds are practically effective against the strains of bacteria of the genus Pseudomonas and Proteus. These known cepahlosporin compounds are also degradable by a .beta.-lactamase which is produced by some resistant strains of bacteria, and they exhibit only a poor activity against some resistant strains of bacteria which have now been a target of clinical treatments of bacterial infections (see: W. E. Wick "Cephalosporins and Penicillins, Chemistry and Biology", edited by E. H. Flynn, Academic Press, New York, N.Y., 1972, Chapter 11.)
We, the present inventors, have already provided a new cephalosporin compound of the general formula ##STR2## wherein R.sup.1 is an amino group or a protected amino group; R.sup.2 is a lower alkyl group, a carboxymethyl group or a protected carboxymethyl group; R.sup.3 is a hydrogen atom, a salt-forming cation or a carboxyl-protecting group; A is an unsubstituted or substituted phenyl group, an unsubstituted or substituted furyl group, an unsubstituted or substituted thiazolyl group or an unsubstituted or substituted 3-lower-alkylthiazolio group, and a pharmaceutically acceptable salt or ester of said cephalosporin compound (see pending U.S. patent application Ser. No. 769,746 and European patent application No. 85 401741.5).
As described above, the cephem antibiotics exhibit strong antibacterial activities against gram-positive and gram-negative bacteria and have low toxicity. Accordingly, they are now employed widely as therapeutic agents for various bacterium-related infections diseases.
Some new problems have, however, arisen such that more resistant strains of bacteria have occurred due to the wide use of the cephem antibiotics, and the recently-developed cephem antibiotics of so-called "third generation" do not show fully strong antibacterial activities against gram-positive bacteria, although their antibacterial activities are high against gram-negative bacteria and resistant strains or bacteria [for example, "Antimicrobial Agents and Chemotherapy" 25, 98 (1984)]. In addition, many of the conventional drugs of cephem type have been developed as parenteral solutions. They are hence accompanied by a serious drawback that their absorpability in living animals are too low to show sufficient effectiveness when administered orally.